Not Applicable
Not Applicable
1. Field of Invention
This invention relates to an apparatus and method for treating water or wastewater, specifically to an apparatus and method for removing insoluble materials such as suspended solids and/or oil from water or wastewater.
2. Description of Prior Art
In current practice, gravity settling clarifiers and dissolved-air floatation (DAF) clarifiers are usually used for removing insoluble materials such as suspended solids and/or oil from water or wastewater. For example, in municipal wastewater treatment plants, gravity settling clarifiers are used for removing suspended solids from wastewater. Gravity settling clarifiers can quickly remove heavy solid particles (those with specific gravities significantly greater than one). However, light solid particles and oil (those with specific gravities close to or less that one) are difficult or impossible to remove by gravity settling. As we know, insoluble materials in water or wastewater have a variety of specific gravities (from less than one to greater than one). Because heavier insoluble materials usually settle before those with lower specific gravities, the overall removal rate of insoluble materials decreases with time. As a result, gravity settling clarifiers are efficient only for removing heavy insoluble materials. It cannot efficiently remove all insoluble materials from water or wastewater, especially those with low specific gravities.
DAF clarifiers are also used for removing insoluble materials from water or wastewater. In this method, the water with high air content is introduced into the water or wastewater. Air is gradually released from the high air content water in a fine bubble form after pressure reduction. The mixture of water, insoluble materials, and fine air bubbles then enters a DAF separation tank. Fine air bubbles may attach onto the surface of insoluble materials (solid particles and/or oil droplets). With the help of the attached fine air bubbles, insoluble materials float upward or remain on top of the water surface in the DAF separation tank. Thus, the water or wastewater is clarified. The accumulated floating sludge is then removed from the DAF separation tank.
DAF clarifiers are preferable for removing insoluble materials with low specific gravities. However, insoluble materials in water or wastewater have various specific gravities. Some heavy solid particles that can be easily removed through free gravity settling will now remain in suspension as effects of attached fine air bubbles. Therefore, these solid particles will not be removed. As a result, DAF clarifiers are inefficient for removing all insoluble materials from water or wastewater, especially those with high specific gravities. Although the DAF separation tank usually has a sludge hopper to collect the settled solid particles, these solid particles could be removed much faster without the interference of attached fine air bubbles in the DAF process. Water or wastewater contains various insoluble materials that have different specific gravities. Ideally, heavy solid particles should be removed by gravity settling, while light solid particles and/or oil should be removed by DAF. However, current clarifiers only have one clarification mechanism.
Objects and Advantages
Accordingly, the objects and advantages of my invention are to provide an integrated apparatus that contains both the gravity settling mechanism and the DAF mechanism in a compensating manner for effectively and efficiently removing both heavy and light insoluble materials from water or wastewater. Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
The invention is an apparatus that contains both the gravity settling mechanism and the DAF mechanism in a compensating manner. It comprises a gravity settling chamber for the removal of heavy solid particles, a DAF chamber for the removal light solid particles and/or oil, a chamber connection channel that connects said gravity settling chamber and said DAF chamber, an air-dissolving device for generating high air content water, an effluent collection device, and a water level control device. During the treatment, water or wastewater first enters the gravity settling chamber for the removal of heavy solid particles by gravity settling. The pre-settled water with the remaining solid particles and/or oil then enters the DAF chamber through said chamber connection channel for DAF separation. High air content water is introduced into the chamber connection channel and mixes with the water or wastewater that contains only light solid particles and/or oil. Light solid particles and/or oil are then floated upward or maintained on top of the water surface in the DAF chamber by the attached fine air bubbles released from the high air content water. The clarified water then flows downward to the effluent collection device.
In the apparatus of this invention, heavy solid particles are removed by gravity settling while the remaining light solid particles and/or oil are removed by floatation. Since both the gravity settling mechanism and the DAF mechanism are integrated in a compensating manner, the performance of the apparatus of this invention is enhanced compared with conventional clarifiers that employ only one clarification mechanism. As a result, both heavy and light insoluble materials in water or wastewater can be effectively and efficiently removed.
In cases where chemicals such as coagulant and flocculants are needed to enhance the removal of insoluble materials and some soluble materials, a mixing device needs to be installed in connection with the inlet. Chemicals need to be injected into the water or wastewater at points before the mixing device so that the chemicals can mix with the water or wastewater at the mixing device. The mixture then enters the gravity settling chamber and subsequent DAF chamber for clarification. In this case, the gravity settling chamber also acts as a flocculation chamber.